This invention relates to a governor for use in controlling the rate at which fuel is supplied to a fuel pump, and thus for use in controlling the operation of an engine of the compression ignition type.
A governor for use with a diesel engine of an alternator and generator set typically includes a centrifugal weight mechanism arranged to rotate at a speed associated with engine speed and to act upon a spring biased lever. The lever is coupled to an angularly movable fuel metering valve such that movement of the lever is transmitted to the valve to adjust the setting of the valve. In particular, the governor is arranged such that, in the event that the load on the engine changes, a corresponding change in the fuelling of the engine is made to control the engine in such a manner that it operates at a substantially constant speed. It is known to provide the lever of the governor with a stabiliser device or damping arrangement which serves to damp oscillations of the engine under certain load and fuelling conditions which can otherwise adversely affect operation of the governor.
In order to permit the governor to be adaptable for use in, for example, different types of engine and with different types of engine fuel pump, the governor is arranged such that the governor arm has a longer stroke than is required to give the necessary variation in fuelling level. The metering valve is therefore moved through a region of xe2x80x9cdead travelxe2x80x9d, in which no variation in fuelling occurs, before the region of travel in which a variation in fuelling does occur is reached. However, if the lever arm is provided with a damping arrangement, movement of the metering valve through the region of dead travel can cause an undesirable delay in the change of fuelling from the maximum fuel setting to that necessary to achieve the desired speed upon engine start up.
Furthermore, in internal combustion engines provided with an overspeed protection device which is arranged to trip so as to halt engine operation in the event that the engine speed exceeds a predetermined, maximum safe speed at a given rate of engine rotation, any delay in control of fuelling due to movement of the metering valve through the region of dead travel can cause the overspeed protection device to trip inadvertently upon engine start up. As a result, engine operation may be halted in undesirable circumstances.
It is an object of the present invention to provide a governor which alleviates this problem.
According to the present invention, there is provided a governor for use in an engine provided with an overspeed protection device arranged to trip in the event that engine speed exceeds a predetermined speed, the governor comprising a centrifugal weight mechanism comprising at least one weight coupled to an angularly adjustable metering valve member through a lever member, the metering valve member being operable to control the level of fuelling of the associated engine, the governor further comprising a damping arrangement associated with the lever member which is arranged to damp oscillatory movement of the lever member, in use, and prevention means for preventing the overspeed protection device associated with the engine tripping upon engine start up.
The engine typically comprises a drive shaft which is arranged to rotate at a speed associated with the engine, the or each weight being pivotable with respect to and rotatable with the drive shaft, the or each weight being arranged to engage a washer member which is interposed between the or each weight and a thrust sleeve member which is cooperable with the lever member such that pivotal movement of the or each weight results in axial movement of the thrust sleeve member and, hence, pivotal movement of the lever member.
The metering valve member is arranged to have a range of travel including a region of dead travel in which substantially no variation in fuelling of the engine occurs.
In one embodiment of the invention, the prevention means comprise means for limiting the range of travel of the metering valve member.
The means for limiting the range of travel of the metering valve member may take the form of an adjustment member associated with the lever member, the adjustment member acting on the lever member so as to limit the extent of movement of the lever member and, hence, the extent of angular movement of the metering valve member.
Typically, the adjustment member may take the form of an adjustment screw. Preferably, the adjustment screw is adjusted such that the metering valve member does not move through the region of dead travel upon engine start up.
The invention provides the advantage that, as the extent of movement of the metering valve member is limited to only that region for which a variation in fuelling occurs, there is no delay in control of fuelling upon engine start up. Hence, inadvertent tripping of the overspeed protection device is avoided.
The invention also provides the advantage that the governor can be adapted for use in engines of different type and with different kinds of engine fuel pump. It can also be adjusted to compensate for manufacturing tolerances and can be adjusted throughout the service life of the governor to compensate for wear.
The adjustment member may be arranged to act directly on the lever member, or may be arranged to act on the damping arrangement associated with the lever member.
Preferably, the governor is provided with first resilient bias means for urging the thrust sleeve member towards the thrust washer member upon engine start up. Typically, the first resilient bias means take the form of a first spring which may be arranged to act on the thrust sleeve member through the lever member.
The provision of the first resilient bias means provides the advantage that, even though the metering valve member is at the end of the region of dead travel upon engine start up, the weights adopt their radially innermost position.
The governor preferably comprises further resilient bias means which serve to urge the lever member against the thrust sleeve member, thereby serving to urge the thrust sleeve member towards the or each weight. The further resilient bias means typically take the form of a further spring.
The provision of the further spring serves to urge the lever member into engagement with the thrust sleeve member such that, upon engine start-up, the thrust washer member rotates with the or each weight.
The damping arrangement may take the form of a hydraulic damping arrangement which may comprise a damping piston, a working chamber for receiving a fluid, whereby fluid pressure within the working chamber acts on a surface associated with the damping piston, and a restricted outlet for permitting fluid to flow into and out of the working chamber at a relatively low rate.
Preferably, the damping piston is slidable within a bore provided in a housing against a damping spring means, the bore defining a working chamber for receiving a fluid which applies a force on the damping piston to oppose the damping force.
The damping arrangement may include an anchor member which is adjustable to vary a pre-load of the damping spring means.
In one embodiment of the invention, the damping arrangement may be provided with by-pass means to permit fluid to flow out of the working chamber at a higher, relatively unrestricted rate, thereby by-passing the restricted outlet and causing the damping arrangement to be disabled.
For example, the damping arrangement may be provided with an additional outlet through which fluid can flow at a relatively unrestricted rate compared to the rate of flow of fluid through the restricted outlet, the damping piston being movable between a first position in which the additional outlet is obscured by the damping piston, in which case the damping arrangement is enabled, and a second position in which the additional outlet is not obscured by the damping piston, the additional outlet thereby providing a by-pass flow path for fluid flowing into and out of the working chamber to disable operation of the damping arrangement.
Preferably, the by-pass flow path may be defined, in part, by a passage provided in the damping piston in communication with the working chamber and whereby, when the damping piston is in the second position, the passage communicates with the additional outlet.
Preferably, the damping spring means is arranged such that the damping arrangement is disabled during movement of the metering valve member through the region of dead travel upon engine start up.
In this embodiment of the invention, as the damping arrangement is disabled upon engine start up when the metering valve member moves through the region of dead travel, inadvertent tripping of the overspeed protection device is avoided.
The damping arrangement may further comprise a further adjustment member for adjusting the damping spring means such that the damping piston occupies a position in which the working chamber communicates with the additional outlet during the dead travel region of the metering valve member.